Curing lights are devices which are used to create a beam of light of an appropriate wavelength to cause curing of photosensitive materials. Various sources of light have been used within curing lights. The source of light may be a halogen bulb, a Xenon bulb, and more recently light emitting devices herein referred to as LEDs.
One of the advantages of using LEDs as the light source arises from the fact that the emission spectrum of some LEDs, in particular, blue LEDs, is in a very narrow band which coincides with the peak of the absorption spectrum of camphorquinone, the most common photoactivator in dental photosensitive materials. Because of the narrow band, almost all of the light energy reaching the material is useful in the process of activating polymerization. No unnecessary heat is applied to the tooth. One of the problems with LED curing lights however is that their light output intensity is relatively low. Because of the low output, LED curing lights are at a disadvantage in the speed of cure as compared with more intense light sources such as halogen bulbs, plasma arc or xenon light sources.
With recent advances in LED technology, there are now available on the market more higher powered individual encapsulated LEDs. One example is the LED sold under the trade mark LUXEON from LUMILEDS™ Lighting LLC. This product can produce up to 500 mW of light output. One of the problems of these types of LEDs is that their light beam is highly divergent, often as much as 160°. This in turn means that much of the light, perhaps as much as 70% will be lost if the LED is coupled directly to a fibreoptic light guide with a typical numerical aperture of 0.5. Numerical aperture is the sine of the acceptance half angle for a particular light guide. A 0.5 numerical aperture means that all rays with a divergence of greater than 30° will not be accepted into the light guide and therefore will be ineffective. If it is desired to compensate for these loses by using a large number of these types of LEDs, their large size, typically 8 mm in diameter, precludes one from doing so since a typical dental light guide has a diameter of not greater than 13 mm with the average being more typically 9 to 10 mm. On the other hand, if used without a light guide, that is, directly at the surface contacting the tooth, it is still not possible to productively use more than one LED of this type because the dimensions of the typical tooth involved would still not be greater than 11×10 mm. Theoretically it is possible to use unencapsulated LEDs, more particularly referred to as dies and pack them more closely in an assembly. However in this case, the light beam becomes even more divergent, typically about 180° and the heat generated from a high number of such dies within the device may create difficulty with respect to cooling. Most existing LED curing lights do not provide a light output intensity of greater than 500 mW/cm2 whereas curing lights using more typical light sources can reach outputs of 2,500 mW/cm2.
Accordingly, there exists a need for a structure which would permit utilization of LEDs as are commercially available, but which are capable of producing the desired light output.